(1) Field of the Invention
The present invention relates to a power steering system and particularly relates to a technique of an abnormality determination of phase open relays attached onto an electrically driven motor providing a steering assistance force for a steering mechanism.
(2) Description of Related Art
In an electrically driven motor installed in a power steering system, phase open relays which are arranged to disable a power supply to the motor are ordinarily disposed in order to prevent a motor burnout due to a failure of a motor drive circuit and to prevent an abrupt stop of the motor due to an electromagnetic brake. Each phase open relay has normally open contacts in a closure state (ON) when the power steering system is in a normal working state. However, when the failure described above is detected, the contacts of each of phase open relays are made open (OFF) so that the power supply to the motor is disabled.
A Japanese Patent Application First Publication (tokkai) No. 2009-261067 published on Nov. 5, 2009 exemplifies a previously proposed abnormality detection technique of phase open means disposed in the power steering system.